Compressed digital-data interactive program system

ABSTRACT

An interactive cable television system is disclosed which utilizes a standard cable television distribution network for simultaneously providing a plurality of viewers with an interactive television program comprising a plurality of signals related in time and content. Video signals are transmitted in a digital format, more than one signal being multiplexed onto a data stream on a single channel. The video signals may be compressed for efficiency. A receiver, in conjunction with a signal selector, selects a particular NTSC channel for playback, then selects a particular video signal from the data stream, and decompresses the video signal for playback. Seamless switching between video signals on different channels is provided. An alternative embodiment is disclosed wherein the various signals which comprise the interactive program are switched at the head end rather than at the receiver. The multiple choice control unit selects a desired signal by relaying the multiple choice selections of the user through a relay box back to a remotely located switching station. The switching station routes the correct video signal down the appropriate cable channel for the particular user.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 08/887,314filed Jul. 3, 1997, which is a continuation of application Ser. No.08/443,607 filed May 18, 1995, now U.S. Pat. No. 5,724,091, which is acontinuation-in-part of application Ser. No. 08/166,608 filed Dec. 13,1993, abandoned, which is a continuation of Ser. No. 07/797,298 filedNov. 25, 1991, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to interactive response systems,and more particularly to an interactive television system which providesinteractive programming using compressed, digital data having more thanone video signal on a broadcast channel, or a multiplexed signal withina digital format, or both.

The invention also relates to seamlessly switching between video signalswhile viewing a first video signal, even though the video signalswitched to may be on a different broadcast channel, or on the samechannel multiplexed with, the currently viewed video signal.

2. Description of the Prior Art

Interactive systems are well known in the art. By synchronizing paralleltracks of an information storage media, and relating the content of thevarious tracks, it was found that interactive activity could besimulated. For example, commonly owned Freeman, U.S. Pat. No. 3,947,972discloses the use of a time synchronized multi-track audio tape to storeeducational conversations. One track is employed to relay educationalinterrogatories to a user, and the remainder of the tracks, selectableby a switching mechanism, are used to convey responsive messages.

These systems progressed to interactive television, wherein multiplebroadcast or cable channels were switched in response to user selectionsto provide interactive operation. Commonly owned Freeman, U.S. Pat. No.4,847,700 discloses an interactive television system wherein a commonvideo signal is synched to a plurality of audio channels to providecontent related to user selectable responses.

Commonly owned Freeman, U.S. Pat. No. 4,264,925 discloses the use of aconventional cable television system to develop an interactive system.Standard television channels with time synchronized content arebroadcast to a plurality of users. Each user switches between channelsresponsive to interrogatories to provide interactivity.

These systems have been tailored to include memory functions so that thesystem can be more interactive, individually responsive, and so thatcustomized messages may be given to the various categories of usersresponsive to informational queries. Freeman, U.S. Pat. No. 4,602,279discloses the use of a memory to store demographic profiles oftelevision viewers. This information is stored to be recalled later forproviding target specific advertising, for example. Prior artinteractive television systems were generally concerned with providingone signal (i.e. one video signal) per channel, whether the channel ison cable television, broadcast television, or a VCR. Because cable andbroadcast television channel capacity is becoming limited as more andmore cable channels are being utilized for conventional programming, andinteractive systems of the type described require multiple channels, itis desirable to reduce the channel capacity required for such systemswhile still providing at least the same level of interactivity.Disadvantages of the prior art are overcome by the present inventionwhich provides an interactive television system which employs multiple,time-synchronized, content-related video signals on one or morebroadcast channels.

SUMMARY OF THE INVENTION

The present invention is an interactive cable television system whichutilizes digital video signals to provide customized viewing responsiveto user selections. A standard cable or direct broadcast satellitetelevision distribution network is utilized for transmitting theinteractive and other programming to users. The present invention allowsa plurality of viewers to be simultaneously provided with a plurality ofdifferent program information message signals related in time andcontent to each other. The interactive program comprises a plurality ofvideo signals related in time and content to one another.

The video signals are converted into digital format for transmission. Ina digital format, it is possible to transmit more than one video signalper cable television channel. Further, it is possible to transmit videosignals via conventional telephone lines. If desired, the variousdigital video signals may be compressed before transmission. Compressionallows an even larger number of video signals to be transmitted over achannel of the transmission media. A multiplexer combines the variousdigital signals into a reduced number of transmission data streams fortransmission. The various NTSC television channels may be allocated in apredetermined fashion to maximize the number of simultaneouslytransmittable signals. The multiplexer in conjunction with thetelevision transmission system multiplexes the desired data streams ontothe desired channels, and transmits these signals over the NTSCchannels. The number of video signals which may be multiplexed onto adata stream on a single transmission channel will vary depending on thevideo signals to be transmitted. The television channels containing adata stream of multiplexed video signals may be transmitted over astandard cable television distribution network, or direct broadcastsatellite transmission system. A receiver receives one or moretelevision channels, some or all containing a multiplexed data stream ofvideo signals or non-multiplexed digital video signals, and inconjunction with a signal selector, selects a particular datachannel/data stream for playback, then selects a particular video signalfrom the data stream's multiplexed signal, and finally expands the videosignal, if necessary, for playback to a television monitor.

A multiple choice controller operates to control the receiver and signalselector to select a particular video signal for playback. If more thanone channel is received, the multiple choice controller may beprogrammed to map the different channels, and the multiple signalsthereon, to a serial numerical channel representation to simplify use bythe user. The signal selector includes the necessary expansion apparatuscorresponding with the compression scheme in use.

In practice, a user selects a desired interactive program to be viewed.Using the multiple choice controller, the user selectably responds toinformation displays or interrogatory messages and the signal selectorselects a particular multiplexed video signal and de-multiplexes,expands and displays the selected video signal. Alternatively, thesignal selector may select a video signal based on personal profileinformation stored in memory.

If more signals are needed for an interactive program than were mappableto a data stream on a single channel, the signal selector in conjunctionwith the receiver is programmed to switch between the various videosignals within a multiplexed data stream as well as between data streamsamong the various broadcast channels to provide the necessary level ofinteractivity.

The various information segments in the various video signals preferablyrelate in real-time and content so that an interactive conversation canoccur as the video signal is played back and the user responds to thevarious interrogatories on the video signals. The use of multiplesignals per channel may be used for many types of interactive programs,including those disclosed in the previously mentioned U.S. Patents, forexample, field synchronized multiple camera angles from a sportingevent, or an interactive game show. However, the present invention alsocovers the use of various video signals not related in real-time andcontent.

In a two-way embodiment, the various signals which comprise theinteractive program may be switched at the head end rather than at thereceiver. This embodiment may be used in a cable television system, adirect broadcast satellite system, a conventional telephone systemmodified to receive digital video signals, or any other appropriatetransmission system capable of sending digital video signals. Themultiple choice control unit, rather than the hand-held multiple choicecontroller, selects a desired video signal by relaying the multiplechoice selections of the user through a relay box back to a remotelylocated switching station, preferably the cable television source. Themultiple choice selections may be relayed to the switching station inany conventional means, such as two-way cable television, telephone, orFM transmission. If the interactive programming is being transmittedover a telephone line, the multiple choice selections may be relayedback over the same telephone line. The switching station receives themultiple choice selection of the user and routes the correct signal downthe appropriate cable channel, telephone line, or other transmissionmedia for the particular user. In such an arrangement, only a singlelink is required between the subscriber or receiver and the head end sothat the one channel link can be used to receive a plurality ofdifferent channel selections dependent on the interactive choice relayedfrom the receiver to the video switch at the head end.

If desired, the two-way link may be used for other purposes, such as totransmit user demographic data back to the programming source forcommercial reasons, or to allow an interactive game show player to winprizes, for example.

The system of the present invention allows improved performance duringswitching, making the channel switches transparent. When a channelchange is required by a user response to an interactive interlude, aslight imperceptible delay is programmed to allow the expansionalgorithm an opportunity to adjust to the rapid change from one videosignal to another.

During the delay, previously obtained video information is displayedwhile the interactive system locates, receives, demultiplexes,decompresses, decodes, and processes the new video signal. This allowsthe interactive system to switch to the new video signal without flickeror distortion appearing on the TV screen, i.e., a seamless switch.

Disclosed are different methods to achieve this seamless switching. Oneinvolves an analog video frame buffer. Another uses two tuners. Otheralternatives include: (a) using two digital video buffers; (b) using alarge memory; (c) using a large buffer in an embodiment similar to thatof (b); and (d) switching at the cable headend.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the Interactive Television System of thepresent invention.

FIG. 2 is a block diagram of the system of the present invention in atwo-way transmission configuration.

FIG. 3 is a block diagram of one embodiment to achieve seamlessswitching between video signals.

FIG. 4 is a block diagram showing an alternative embodiment to achieveseamless switching between video signals.

FIG. 5 is a block diagram showing another alternative to achieveseamless switching between video signals.

FIG. 6 is an alternative method of achieving seamless switching by usingthe memory shown in FIG. 5 as a buffer.

FIG. 7 is an alternative embodiment of achieving seamless switching byswitching channels at the cable headend.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is an interactive television system in which aplurality of viewers are simultaneously provided with a plurality ofdifferent program information message signals. A plurality of videosignals 1 are provided. Video signals 1 may be, for example, variousfield and/or audio synchronized camera angles of a sporting event, or agame show having a content and host acting responsively to userselections. Alternatively, video signals 1 may be any video signalssuitable for interactive conversation, such as those described in U.S.Pat. Nos. 4,847,700, 3,947,972, 4,602,279, 4,264,925, or 4,264,924, thecontents of which are incorporated specifically herein by reference.Various types of time and content related video signals exist which aresuitable for interactive operation.

In previous systems, these various signals would be transmitted to areceiver on separate broadcast or cable channels, each requiring aseparate 6 Mhz NTSC channel. According to the present invention, videosignals 1 are directed to analog-to-digital (“A/D”) convertors 2 whichconvert the various video signals into digital format for transmission.A/D convertors 2 may be of any conventional type for converting analogsignals to digital format. An A/D convertor may not be needed for eachvideo signal 1, but rather fewer convertors, or even a single convertorare capable of digitizing various video signals 1. Interactive videoprograms may also be delivered to a cable or other distribution networkin pre-digitized and/or precompressed format.

Digital conversion results in very large amounts of data. It maytherefore be desirable to reduce the amount of data to be sent, allowingmore signals to be sent over a single transmission channel. For example,a single frame of digitized NTSC video represents over 350 Kbytes ofdata. Therefore, two hours of standard video is about 80 Gbytes. Sincethere are 30 frames/sec in such video, the data transfer rate is 22Mbytes/sec. This large amount of data is preferably reduced by digitalcompression.

In order to reduce the data transfer requirements, the various digitalvideo signals are preferably compressed before transmission. The videomay be compressed by any conventional compression algorithm, the twomost common types being “processor intensive” and “memory intensive.”

The processor intensive approach performs compression by eliminatingnon-changing aspects of a picture from the processing in theframe-to-frame transfer of information, and through other manipulationsof picture information involving mathematical computations thatdetermine the degree to which a given motion in a picture is perceptibleto the human eye. This approach depends on high-speed processing powerat the transmission point.

The memory approach involves division of a picture frame into hundredsof minuscule blocks of pixels, where each block is given a coderepresenting its set of colors and variations in luminance. The code,which is a much smaller increment of information than all theinformation that would describe a given block of the picture, istransmitted to the receiver. There, it calls up the identically codedblock from a library of blocks stored in the memory of the receiver.

Thus, the bit stream represents a much smaller portion of the pictureinformation in this approach. This system is generally limited by thevariety of picture blocks which may be stored in the receiver, whichrelates directly to memory size and microprocessor power.

Examples of commonly known compression techniques which may be used withthe invention are JPEG, MPEG1 and MPEG2.

Data Compressors 3 are provided to reduce the data for each video signalwhich must be transmitted. Data compressors 3 may be of any conventionaltype commonly known in the art for compressing video images, such asthose previously described. Compression of the various video signalsmight be done with fewer data compressors 3 than one compressor pervideo signal. In a conventional analog NTSC system, by way of example,it is customary to transmit one video signal per 6 MHZ channel. Bydigitizing the video signal, it is possible to send a data streamcontaining more than one video signal in one channel. Compressing thedigitized signals, allows even more video signals to be transmitted overa single transmission channel. The number of signals which may be sentover a single channel is generally related to, for example, a) the typeof video being sent; b) the video compression scheme in use; c) theprocessor used and memory power; and d) the bandwidth of thetransmission channel.

Compression techniques exploit the fact that in moving images there isvery little change from frame-to-frame. Editing out the redundanciesbetween frames and coding just the changes allows much highercompression rates. The type of video which normally contains a greatdeal of high-speed movement, such as occurs at live sporting events,will, therefore, have the lowest compression rates. Movies, on the otherhand, which normally have a lower frame rate and less frame-to-framechange than a live sporting event will achieve higher compression rates.Currently, commonly known compression schemes have compression ratesthat vary from 2:1 to 10:1 for satellites, and 2:1 to 5:1 for cabletelevision systems, depending on the degree of motion.

Once the various video signals 1 have been digitized and compressed,multiplexer 4 combines the various digital signals into a reduced numberof transmission data streams for transmission. For example, if 68 NTSCchannels are available, and each channel is capable of transmittingeither 4 digitized, compressed slow moving video signals (e.g. movies)or 2 digitized, compressed, high-speed video signals (e.g. sports), thenthe various NTSC channels should be allocated in a predetermined fashionto maximize the number of simultaneously transmittable signals.

As an example, the broadcast frequency corresponding to a first NTSCchannel may contain a data stream of separate digitally compressednon-interactive movies. On this frequency, the data stream would containvideo signals representing a number of movies. However, the videosignals, unlike those of an interactive program, are not related in timeand content. The frequency corresponding to a second channel mightcontain a digital data stream of an interactive sports program,consisting of two multiplexed compressed high-speed video signals thatare preferably related in time and content. The frequency correspondingto a third channel might contain a digital data stream of an interactivemovie consisting of four multiplexed compressed video signals which arerelated in time and content. The frequency corresponding to a fourthchannel might contain an analog NTSC signal relating to localprogramming. Therefore, using the invention, four NTSC channels couldcontain a channel of multiplexed movies, an interactive sports program,an interactive movie, and local programming.

Multiplexer 4 receives the incoming compressed, digitized video signalsand in a predetermined conventional fashion, in conjunction withtransmitter 5, multiplexes the desired video signal onto the desiredchannels, and transmits these signals over the NTSC channels. CertainNTSC channels may contain only one video or other signal, in analog ordigital form.

As indicated earlier, the number of video signals which may bemultiplexed onto a data stream on a single transmission channel willvary. Also, the number of channels which use data streams may vary. Thetransmission data streams are transmitted by transmitter 4 viatransmission media 6 to a receiving station 7. The transmitter 4, media6, and receiver 7 may be any conventional means for transmitting digitalvideo signals including broadcast television, cable television, directbroadcast satellite, fiber optic, or any other transmission means.Alternatively, the invention may be self-contained in a stand-alonesystem, as explained below.

The transmission means may also be a telephone system transmitting adigital video data stream. Thus, a multiplexed data stream containingseveral broadcast channels or an interactive program with related videosignals may be sent directly to a user over a single telephone line. Theaforementioned digital transmission devices may include means fortransmitting analog signals as well.

In one of the preferred embodiments, the digital transmission signal istransmitted using a cable television system. Receiver 7 receives variousNTSC channels, some or all containing multiplexed or non-multiplexeddigital video signals. Ordinarily, more than one channel will betransmitted by transmitter 5 and received by receiver 7 as in anordinary cable television system. However, each of the differentchannels may have a data stream containing several digitized videosignals thereon. Therefore, receiver 7 preferably operates inconjunction with signal selector 8 to select a particular NTSC channelfor playback, then to select a particular video signal from the datastream's multiplexed signal, and finally to uncompress or expand thecompressed video signal, if necessary for playback to monitor 10.

Multiple choice controller 9 operates to control receiver 7 and signalselector 8 to select a particular video signal for playback. Inpractice, a user need not know that multiple signals per channel are inuse. If, for example, 68 channels with 4 signals-per-channel were inuse, controller 9, in conjunction with receiver 7 and signal selector 8might be programmed to represent these channels to the user as channels12-72. Monitor 10 may be, for example, a conventional television. Signalselector 8 preferably includes a conventional de-multiplexer forselecting a particular video signal from the data stream on the channelcurrently being received by receiver 7. Signal selector 8 furtherincludes the necessary un-compression or expansion apparatuscorresponding with the compression scheme in use by compressors 3.

In practice, an interactive sporting event program might be transmittedon a 6 MHZ cable television signal using a compression-multiplexingscheme which allows two sports video signals (A and B, for example) tobe transmitted over a single NTSC channel (channel 34, for example). Itmight be desired to have four video signals (A-D, for example) for theparticular interactive sporting event. A first video signal (signal A)may contain the standard broadcast signal of the game; the second videosignal (signal B) may contain a close-up view of the game action; athird video signal (signal C) may contain a continuously updated replayof game highlights; the fourth video signal (signal D) may containstatistical information. These four video signals (A-D) may, forexample, be multiplexed as follows: video signals A and B multiplexedonto a data stream transmitted on cable channel 34; video signals C andD multiplexed onto data stream transmitted on cable channel 35.Alternatively, all four video signals (A-D) could be multiplexed intoone data stream carried on one frequency channel. These four signalsmay, however, be mapped by controller 9, or signal selector 8, to playas separate channel displays for the user which, when the viewer makeschoices on the multiple choice controller, a seamless switch occurstherebetween. Each video signal of this interactive program may includea label which reads, for example, “Full-Screen Action—Press A: Close-upAction—Press B: Replay—Press C: Statistics—Press D.”

As shown, if more signals were needed for an interactive program thanwere mappable to a data stream on a single channel, signal selector 8 inconjunction with receiver 7 may be programmed to switch between thevarious video signals 1 as well as the various broadcast channels toprovide the necessary level of interactivity. However, preferably allthe various video signals associated with a particular interactiveprogram are multiplexed onto a single channel.

Additionally, the signal selector 8 may store information relating tocurrent and previous user responses. For example, the personal profileof the viewer or previous response patterns of the viewer could bestored in memory. This information may be used in conjunction withcommands transmitted within the video signals, as discussed in U.S. Pat.No. 4,602,279, incorporated herein by reference. The stored personalprofile information and received commands may be used to switchinteractively between data streams and video signals without anyadditional response from the user.

The multiplexed interactive program may be transmitted over a singletelephone line, if desired. In this embodiment, multiple choicecontroller 9 is programmed to switch between the various video signalson the single telephone line. If additional channels were desired, atwo-way configuration is used as described below.

The system of the present invention may be utilized in an educationalembodiment. In this embodiment, information is stored on each datastream in a plurality of reproducible information segments, each ofwhich comprises a complete message reproducible by the receiver directlyin response to the selection of the video signal by signal selector 8responsive to a user selection on multiple choice controller 9. Each ofthe information segments in the various data streams containinterrogatory messages with associated multiple choice responses,responsive messages, informational messages, or combinations thereof.

The various information segments in the various data streams preferablyrelate in real-time and content so that an interactive conversation mayoccur as the video signals are displayed and the user responds to thevarious interrogatories contained in the video signals. As a useranswers a particular interrogatory with a multiple choice response, theinformation in the video signal associated with the particular selectionis displayed by the signal selector 7. The various interrogatories,responsive messages, and informational messages may generally becontained in any one, more than one or all of the various video signals.

The use of a data stream containing multiple video signals per broadcastchannel may be used for many types of interactive programs, such asthose disclosed in the previously mentioned U.S. patents. Otherinteractive programs may be developed which are within the scope of thepresent invention.

The present invention may also be utilized as a stand-alone system withno transmission means necessary. In this embodiment, the digitized videosignals that make up an interactive program are stored in local storagemeans such as video tape, video disk, memory (e.g., RAM, ROM, EPROM,etc.) or in a computer. Preferably, the digital video signals aremultiplexed onto a standard NTSC signal. The particular storage meansmay be connected to any of the interactive boxes disclosed in FIGS. 3-5,and described below. The interactive boxes would then be connected to atelevision set. Alternatively, the circuitry in FIGS. 3-5 below could beimplemented on a board and inserted into a standard personal computer(PC). A separate microprocessor on the interactive board is notnecessary for this configuration since the standard PC processorperforms the functions of the processor 108 shown in FIGS. 3-5.

As shown in FIG. 2, the system of the present invention may be operatedin a two-way configuration. In this mode, the various video signals 1are processed as previously described, being digitized by A/D convertor2 and compressed by video compressors 3. The signals are then routed toa central switching station 14. In this embodiment, the switchingbetween the various video signals is accomplished at the head end ratherthan at the receiver. Multiple choice control unit 9 relays the multiplechoice selections of the user through a relay box 17 back to theremotely located switching station 14. The multiple choice selectionsmay be relayed by relay box 17 to the switching station by anyconventional means, such as two-way cable television, telephone, or FMtransmission. Switching station 14 receives the multiple choiceselection of the user and routes the desired signal to transmitter 5which conventionally transmits the desired video signal down theappropriate cable channel for the particular user. If desired,transmitter 5 may also transfer conventional programming on the cabletelevision channels not being used for interactive programming.Alternatively, switching station 4 may include multiplexing equipment aspreviously described, and thus operate multiple interactive ornoninteractive programs over a single television channel.

For example, if it were desired to implement the interactive footballgame program as previously described, a single NTSC cable channel may beallocated for the program. However, in this instance, the video signalswould be present at the transmitting end. In response to a signal fromwireless controller 9, a signal is sent by relay box 7 to the cable TVswitching station which routes the desired video signal to therequesting viewer. Such a system requires very fast switching equipment,but can be implemented using digital imagery.

Alternatively, it may be desirable to transmit the interactive sportingevent over a single telephone line. When the user enters a selection oncontroller 9, a signal is sent via the telephone line to the centralswitching station which routes the desired signal of the interactiveprogram over the user's telephone line so that a single link handlesboth the interactive choice being made at the receiver and thetransmission of that choice, out of a plurality of choices, from thehead end where the actual switching takes place in response to theinteractive selection made at the receiver.

The two-way link between the user and the switching station may be usedfor other purposes. For example, demographic data may be transferredfrom the user to the broadcast network for commercial purposes, such astargeted advertising, billing, sending a game show winner a winningnumber for pickup of a prize, or other commercial or non-commercialpurposes.

As previously described, compression systems generally perform lessefficiently when frame-to-frame content includes many changes in pixelcontent (e.g., during fast motion or scenery changes). The system of thepresent invention may be advantageously programmed to ease theprocessing burden on the uncompression program. When a key on thecontroller is depressed to select a desired signal, a slightimperceptible delay may be effectuated if desired. This delay allows theuncompression or expansion algorithm a short period of time to adjust tothe rapid change from one video signal to another which ordinarilycauses a degradation in the efficiency of the algorithm causing videoglitches to appear on the screen display.

As shown in FIG. 7, a two way link (similar to FIG. 2) may also be used,employing virtual channels back to the user. In this embodiment,multiple video signals, preferably related in time and synchronous toeach other, are present at a cable headend 300 on multiple channels A,B. C, . . . N of a video signal bus 250. The signals may be locallygenerated or received from a remote location (such as a sporting arena)by receivers 200, 202, 204, and 206. Alternatively, if the remotelyreceived signals are digitally multiplexed onto one channel, a digitaldemultiplexer would replace receivers 200-206 and would demultiplex thesignals and place each signal on a separate bus channel. The local orremote signals are synchronized by sync circuit 208. A number of remotecontrol interactive switches 210, 212, 214, 216, and 218 are connectedto video signal bus 250. The multiple channels on bus 250 are providedsynchronously and simultaneously to the series of remote controlinteractive switches 210, 212, 214, 216, 218. These remote controlinteractive switches are dynamically allocated to users who requestaccess to an interactive program. Each switch is connected to afrequency agile modulator 220, 222, 224, 226, 228 to assign the switch avirtual channel in order to connect a signal from bus 250 to a specificuser at a remote site. Each switch is assigned to a single user so thenumber of switches present at the headend is the limiting factor to thenumber of users who can interact simultaneously. If it is assumed thatonly a portion of the users will interact simultaneously, an algorithmis used to determine the optimum number of remote switches necessary toassure an acceptable percentage of access.

After passing through the frequency agile modulators 220, 222, 224, 226,228, the signals from video signal bus 250 progress through the cable(or broadcast TV) system 260. The signals may pass through RF feed 262and amplifier 230. The user's set top box 232, 234, 236, containing afrequency agile demodulator, is tuned to the frequency of the associatedfrequency agile modulator 220, 222, 224, 226, 228. The decoded signalfrom the set top box 232, 234, 236 is displayed on television monitor10.

When a user desires to interact, the user issues a command on thecontroller 9. The command is received by the set top box 232, 234, 236.A user request is sent back down the cable or other transmission system260 to one of the remote switches 210, 212, 214, 216, 218. At theappropriate time, based on the user request and the algorithm forinteractivity which accompanies the program, the remote switch makes acut during a vertical blanking interval from one signal on bus 250 toanother signal on bus 250. The result of this switch is modulated by oneof the frequency agile modulators 220, 222, 224, 226, 228 and sent downthe virtual channel to the user, who sees a seamless cut from one imageto the other as a result of the interaction. The signal delivered to theuser may be full bandwidth or compressed video. Likewise the videosignal on the bus 250 delivering the simultaneous signal to the multipleremote switches 210, 212, 214, 216, 218 may be compressed video. Thisembodiment allows for a relatively low cost remote user box because themost costly switching equipment is located at the headend and eachremote switch may be allocated to any user. Therefore, the cost isspread over the larger population of users.

As an example, it is assumed that the signal received by receiver 206 isplaced on bus line 270 of the video signal bus 250 and is forwarded toset top box 236 and displayed on monitor 10. At some point the set topbox 236 causes a user request to be generated. The user request is basedon a current or past entry on controller 9 and/or information stored inset top box 236 (e.g., information stored could be previous userresponse information or personal profile information). The cable TVsystem 260 may amplify the user request at amplifier 230 while carryingthe user request back to frequency agile modulator 226, whichcommunicates the request to remote switch 216. During the verticalblanking interval, the remote switch 216 disconnects from old bus line270 and switches to the appropriate line on the video signal bus 250, inthis example line 280, based on the user request. This is shown by thedotted-line connection at 290. The signal from the new connection(received by receiver 204) is sent through the frequency agile modulator226 on channel 47 and the cable TV system 260 to the user's set top box236. The new signal is seamlessly displayed on television monitor 10,without any switching occurring at set top box 236.

As alternatives to the cable headend 300 and cable TV 260 of FIG. 7, atelephone central office and/or telephone lines may be used. Thisalternative would allow the set tops 232, 234, 236 to receiveinteractive programming from a telephone company or cable headend viatelephonic communication.

FIGS. 3-6 show preferred embodiments of the receiver 7 and signalselector 8 of the present invention to enable seamless flicker-freetransparent switching between the digital video signals on the samechannel or different channels. These embodiments may be connected to anytransmission media or simply connected to the output of any stand-alonestorage means for the digitized multiplexed interactive program.Preferably, the receiver 7 and signal selector 8 are both components ofan interactive program box 11, which connects to a television or otherdisplay monitor. Alternatively, the required functionality of the RFreceiver 7, signal selector 8 and monitor could all be combined in astandard personal computer by the addition of a few components to thepersonal computer. To provide this capability, only an RF demodulatorboard, digital demultiplexer, decompressor(s), frame buffer(s), and synccomponents need to be added to the personal computer. These items, andany other components, may be connected to the PC processor and storageelements as disclosed in FIGS. 3-5. In this embodiment, the user makesselections via the computer keyboard.

FIG. 3 shows an embodiment with a single analog frame buffer. FIG. 4includes pairs of RF demodulators, error correctors, and demultiplexersand/or a pair of digital video buffers, as described below. FIG. 5utilizes a single digital multiframe memory. FIG. 6 is directed to analternative method of using the memory 190 described in FIG. 5, anddepicts buffering the memory contents over time. Similar circuitelements appearing in FIGS. 3-5 are referred to by using the samereference numbers.

FIG. 3 shows an embodiment which allows for a seamless video switchbetween two or more separate digital video signals. As shown in FIG. 3,a microprocessor 108 is connected to RF demodulator 102 and digitaldemultiplexer 106. The microprocessor 108 directs demodulation anddemultiplexing of the proper channel and data stream to obtain thecorrect video signal. The proper channel is determined either byexamination of the user's input from user interface 130 and/or any otherinformation or criteria (such as personal profile information) stored inRAM/ROM 120. For example, the RAM/ROM 120 could store commands providedwithin the video signals as discussed in U.S. Pat. No. 4,602,279, andincorporated herein by reference. The user interface 130 may be aninfrared, wireless, or wired receiver that receives information frommultiple choice control unit 9.

The RF demodulator 102 is part of the receiver 7, and demodulates datafrom the broadcast channel directed by the microprocessor 108. After thedata stream is demodulated, it passes through a forward error correctioncircuit 104 into a digital demultiplexer 106. The demultiplexer iscontrolled by microprocessor 108 to provide a specific video signal outof a number of video signals which may be located within the data streamon the demodulated broadcast channel. The demultiplexed video signal isthen decompressed and decoded by decompressor/ decoder 110. Thedecompressor/decoder 110 includes a digital to analog converter toconvert the decompressed signal into an analog signal. The analog videosignal is synchronized by a sync add circuit 150 and a sync generator140. The analog video signal is then buffered by an analog video framebuffer 160. The buffered video signal is modulated by a modulator 170into a NTSC compatible signal.

By using an analog video frame buffer 160 and delaying the viewing of agiven signal, enough time is allowed for the decompressor/decoder 110 tolock onto, decompress, convert to analog, and wait for the resultantvertical interval of a second video signal. For example, assume videosignal A is currently being processed and transferred through thecircuit shown in FIG. 3 and displayed on the television set or monitor10. Based upon a user selection, the microprocessor 108 directs thedigital demultiplexer 106 and RF demodulator 102 to switch to anothervideo signal, video signal B. To accomplish this, the analog video fromthe first digital video signal, video signal A, complete with videosync, is fed into analog video frame buffer 160. This buffer can holdthe full video picture for “n” number of frames after which the signalis output to the display. In effect, a delayed video signal A is viewed“n” number of frames after the signal has been received by thetelevision receiver. When the user selects a different video path bymeans of pressing a button on a keypad, the microprocessor instructs thedigital demultiplexer 106 to stop decoding signal A and lock onto signalB to begin decoding signal B instead of signal A.

While this is happening, even though the decompressor/decoder 110 is nolonger decompressing video signal A, the display is still showing videosignal A because it is being read from the buffer 160. As soon asdecompressing and decoding occurs, the microprocessor 108 looks for thenext vertical blanking interval (VBI) and instructs the analog videoframe buffer 160 to switch to its input, rather than its buffered outputat the occurrence of the VBI.

Since the RF demodulator 102, forward error corrector 104, digitaldemultiplexer 106, and decompressor/decoder 110 require a certain timeperiod to decompress and decode the video signal B frame from its datastream, the size of the buffer 160 has to be large enough so that thisprocessing can take place without interruption during the switching ofthe video signals. If desired, the system may continue to use the buffer160 in anticipation of a future switch. By using the microprocessor 108to manipulate the fill and empty rate of the buffer 160, the buffer 160may be rapidly filled with video signal B frames and then after a periodof time will be reset and ready to make another switch to another videoin the same manner. The buffer 160 may also be reset by skipping framesor providing a delay between sequential frame outputs for a short timein order to fill the buffer 160. If a delay is used to maintain videosignal or frame output while the buffer 160 is being filled a slightdistortion may occur for a brief amount of time.

Because a first video signal is always displayed as the output of thebuffer after the delay, the buffered video masks the acquisition anddecoding of a second video signal. As long as the buffer is large enoughto keep the first video running while the second video is beingdecompressed and decoded, a seamless switch will occur.

FIG. 4 shows an alternate, dual tuner embodiment for seamless switchingbetween separate video signals. In this embodiment, the microprocessor108 controls the selection of the RF channel that is demodulated by RFdemodulators 102A, 102B. The demodulated data streams enter the forwarderror correctors 104A, 104B. At the output of the forward errorcorrectors, the data streams are transmitted to the input of the digitaldemultiplexers 106A, 106B.

As with the RF demodulators 102A, 102B, the digital demultiplexers 106A,106B are controlled by the microprocessor 108. This configuration allowsthe microprocessor 108 to independently select two different individualtime-multiplexed video signals on different channels and data streams.If all the video signals of an interactive program were contained on asingle channel or data stream, it would only be necessary to have asingle RF demodulator, forward error corrector, and digitaldemultiplexer serially connected and feeding into the two digital videobuffers.

Two data streams are provided from the digital demultiplexers 106A and106B. One data stream carries video information pertaining to the videosignal the user is currently viewing. The second data stream carries thevideo signal selected based on the user's previous and/or currentinteractive selections from the user interface 130, as determined by themicroprocessor 108.

The digital information on each of the two streams is buffered indigital video buffers 164, 165. The buffered signals are thendecompressed and converted into analog signals by decompressors/decoders 110A, 110B which include digital to analog converters. Thedecompressors 110A, 110B are preferably MPEG decoders.

A local sync generator 140 is connected to sync add 151, 152 and framesync 153, 154 circuits. Because both streams are synchronized based onsignals from the same local sync generator 140, each stream becomessynchronized to the other. In particular, the signals on each stream areframe synchronized.

A vertical blanking interval (VBI) switch 180 is connected to themicroprocessor 108 so that the input may be switched during the verticalblanking interval of the current stream, resulting in a seamless switchto the viewer.

The embodiment of FIG. 4 operates as follows. Based on user responsesand control codes, it is assumed that the microprocessor 108 determinesthat a switch from video signal A to video signal C should be performed.RF demodulator 102A and digital demultiplexer 106A are processing thecurrently viewed video signal, video signal A, which is progressingthrough the upper branch components 164, 110A, 151, 153, 180. A commandis issued from the microprocessor 108 to the RF demodulator 102Bcommanding a switch to the channel and data stream on which video signalC is located. The microprocessor 108 also instructs the digitaldemultiplexer 106B to provide video signal C from the received datastream to digital video buffer 165.

At this point, RF demodulator 102A and digital demultiplexer 106A arestill independently receiving and processing video signal A, whichcontinues through the upper branch of the circuit.

At a certain point, the digital decompressor/decoder 110B in the lowerbranch will begin filling up with video C frames. After the video signalC is decompressed and decoded, it is converted into analog. A local syncgenerator 140 inserts both local sync and frame sync to video signal Cvia sync add circuit 152 and frame sync circuit 154 in order tosynchronize it with the currently displayed video signal A, which isstill being provided from digital video buffer 164. At the appropriateswitch point, triggered by programming codes supplied with each videosignal A and C, the microprocessor directs the VBI switch 180 to switchin the vertical blanking interval from video A to video C, at which timevideo C will then seamlessly appear on the television set monitor 10.

Digital video buffers 164 and 165 may be used in the circuit of FIG. 4,but are optional. However, in an alternative embodiment the buffers 164and 165 would be required to provide a seamless switch if the FIG. 4circuit was modified to incorporate a single RF demodulator 102, singleforward error corrector 104, and single digital demultiplexer 106 (as inFIG. 3), each with a single input and single output. In this alternativeembodiment, the circuit cannot independently receive and demultiplex twodata streams on different frequency channels. One buffer is used tostore previously received video signals, while the other buffer quicklypasses through the selected video signals.

Based on the same assumptions above, video signal A is progressingthrough the upper branch of the circuit and it is desired to switch tovideo signal C. However, in this alternative embodiment, digital videobuffer 164 is providing maximum buffering to video signal A.

Because it is desired to switch to video signal C, microprocessor 108directs the alternative circuit (containing a single RF receiver 102,single forward error corrector 104 and single digital demultiplexer 106connected in serial), to receive and demultiplex the data stream onwhich video signal C is located, which may be different than that ofvideo signal A. When video signal C is demultiplexed, the microprocessor108 directs digital video buffer 165 to provide minimum buffering ofvideo signal C so that decompressor/decoder 110B may quickly decompressand decode the digital signals. After decompression and decoding, videosignal C is synchronized with video signal A. At this time video signalA is read for display from digital video buffer 164. The digital videobuffer 164 must be large enough to provide video frames for outputduring the time it takes the RF demodulator and digital demultiplexer toswitch to video signal C and the time required for decompression,decoding, and synchronization of video signal C.

When video signal C is synchronized with video signal A, themicroprocessor directs VBI switch 180 to switch from video signal A tovideo signal C in the vertical blanking interval of video signal A,thereby providing a seamless and flicker-free switch.

At this time, digital video buffer 165 will begin to utilize maximumbuffering by altering its fill/empty rate as described above withrespect to the FIG. 4 embodiment. When adequate buffering is achieved, aswitch to another video signal may be performed in the same manner asdescribed above.

Another preferred embodiment is shown in FIG. 5. This embodiment alsoincludes an RF demodulator 102, a forward error corrector 104, and adigital demultiplexer 106. However, the circuitry differs along the restof the chain to the television set or monitor 10. In this embodiment, alarge memory 190 is incorporated and connected to the output of thedemultiplexer 106 for storing the compressed composite digital videosignal. The decompressor/decoder 110 is inserted at the output of thecompressed memory 190. The decompressor/decoder 110 decompresses thedigital signal, converts the signal to analog and forwards the analogsignal to the RF encoder 170 for transmission to the monitor 10. Oncethe composite compressed digital video signal is fed into the compressedmemory 190, the microprocessor 108 directs a pointer to be placedsomewhere along the compressed digital video signal. Based on theplacement of the pointer, different frames and different segments of thecomposite digital video signal will be read from memory 190 fordecompression and decoding.

The different video signals are distinguished from one another becausethey are labeled, preferably by headers. Assuming that video signal Ahas been selected for play on the monitor 10, the compressed digitalmemory 190 fills up with A frames. Assuming a switch to video signal Cis desired, the microprocessor 108 directs the RF demodulator 102 anddigital demultiplexer 106 to begin filling the compressed memory 190with video C frames. The decoder pointer begins to move down. As soon asa sufficient number of C frames have entered the compressed memory 190,the pointer will then jump to the beginning of the C frames. The Cframes are then output into the decompressor/decoder 110 where thedigital frames are converted into an analog signal.

The digital video is multiplexed in a series of easily identifiablepackets. These packets may contain full compressed frames of video (Iframes) or may include only the differences between full frames (Bframes or P frames). To be able to reconstruct the full video images,the decompressor/decoder 110 needs to have a minimum number of I, P andB frames. In this embodiment the buffer memory 190 is filled withcompressed packets from a given stream of data including I, B and Fframes. When the microprocessor 108 instructs the digital demux 106 tostart sending packets from a different data stream there is no way to becertain that the next packet will be an I packet needed for decoding thesecond video stream. To avoid a breakup of the video images, which wouldoccur if the decompressor, decoder 110 suddenly started receivingpackets unrelated to the stream it was decoding, the microprocessor 108starts to fill up the memory 190 with video signal C packets until it isdetermined that a full sequence of I, B and P frames are available. Assoon as the valid sequence is in memory the microprocessor 108 moves thememory read pointer to the start of a valid sequence of C video signalpackets so that the decompressor decoder can successfully decode the Csignals. This results in a seamless switch from video signal A to videosignal C.

This embodiment requires a data channel for enabling a synchronousswitch between a first video stream and a second video stream. This datachannel comprises the ACTV codes which link together the differentprogram elements and information segments on the different videosignals. In addition, the data channel also comprises synchronizationpulses and a time code to signify to the pointer the proper time to skipfrom a memory location representing one video signal to a memorylocation representing another video signal in order to enable a seamlessswitch.

The microprocessor 108 reads the data signal from the digitaldemultiplexer 106 and communicates pertinent data to the sync addcircuit 150, which is connected to sync generator 140. Themicroprocessor 108 is then able to synchronously communicate with thememory 190.

The time code sent will identify the timing for one picture, as well asfor multiple pictures, and will lock the different pictures together.This is done through the use of similar clocks at both the transmissionend and the receiver. A time code is used in order to keep the twoclocks at both the transmission and receive end synchronously connectedto one another. Once the clocks at both ends are working synchronously,each of the multiplexed video streams must be synchronized to theclocks. In order to synchronize the multiplexed video stream to theclocks, each of the individual channels must be referenced to a commonreference point and must be identified.

In the preferred embodiment, a packet header would be incorporated intothe transport layer of the MPEG signal to identify the various channels.The packet header will also include information as to where to insertthe vertical blanking interval. In MPEG, the vertical blanking intervalis not transmitted from the headend. Therefore, the vertical blankinginterval must be generated locally. The packet header eye will identifyat what time the vertical blanking interval is in existence in order toeffectuate a seamless switch between analog pictures.

In summary, the combination of clock and the information imbedded ineither the transport layer of MPEG or in a separate packet on a separatedata channel effectuates the linking between each video signal and acorresponding time point. The data channel also includes informationdesignating when all the various video signals will be in synchronismwith one another. It is at these points that the microprocessor 108 maydirect the pointer to skip from one location to another location, at atime (such as during the VBI) when a seamless switch will result.

FIG. 6 shows a method to use the memory 190 described with respect toFIG. 5. FIG. 6 shows a timed sequence of video signals that are storedin the memory 190. In FIG. 6, the decompressor/decoder 110 requires, forexample, five specific video frames before decompressing and decodingcan begin. Specifically, the decompressor/decoder 110 requires framesA,a,a,a,A, B,b,b,b,B, or C,c,c,c,C, and so forth. Because of the MPEGcompression algorithm used, certain frames of video signals (representedby the lowercase letters) cannot be decoded and decompressed withoututilizing information within certain other compressed frames(represented by uppercase letters).

At time T0 the viewer is watching channel A, the memory is filled withframes relating to channel A, and the pointer is pointing to frame A₁.At time T1, A₁ has been output to the decompressor/decoder 110 and themicroprocessor 108 has switched to channel C. As with a buffer, thememory contents are shifted so that new data c₁ is stored and data a₂ isready for output to the decompressor/decoder 110, because the pointer islocated at a₂. At this point in time, the microprocessor 108 ismonitoring the data as it arrives to determine when data relating tochannel C is present. At time T2, c₂ is stored, and the memory contentsare shifted so that a₃ is ready for output. At time T3, C₃ is read intothe memory and the contents are again shifted so that a₄ is ready foroutput. The pointer position is unchanged.

At time T4, compressed video signal c₄ is stored. The A₅ frame ispresented for output at the pointer location. At time T5, c₅ is stored,while the data is again shifted and a₆ is ready for output.

In this example, the microprocessor 108 immediately recognizes channel Cdata c₆ and C₇ at times T6 and T7, and continues to shift the data inmemory without moving the pointer. Therefore, channel A data frames a₇and A₈ are output to the decompressor/decoder 110. At time T8, there isenough channel C data to begin a decoding sequence, assuming that thedecompressor/decoder 110 requires three frames (c,c,c) which referencetwo frames (C,C) for decompression and decoding purposes. Therefore, attime T8, the pointer is moved to point to frame C₃, which will be thenext frame output to the decompressor/decoder 110. Frame C₃ is used inthe decompression and decoding of one or more of frames c₄, c₅, and c₆.

Rather than outputting the compressed video signals individually, thegroup of C₃, c₄, c₅, c₆, and C₇ may be output to thedecompressor/decoder 110 at once. This is the preferable technique whereC₇ is required to decode preceding frames (i.e. c₄, c₅ or c₆).

As with the examples described previously and shown in FIGS. 3 and 4,the buffer may alter its fill and empty rates to provide maximumbuffering. If this is performed, the pointer will be reset to itsoriginal position, as shown in FIG. 6 at time Tn.

Using FIGS. 3-6, and the previous description of memories and buffers,the artisan will be able to provide a seamless switch for flicker-freeswitching between interactive channels of the interactive televisionsystem of this invention. Other variations using the above schemes arealso possible, as realized by the artisan of ordinary skill.

Although the present invention has been described in detail with respectto certain embodiments and examples, variations and modifications existwhich are within the scope of the present invention as defined in thefollowing claims.

What is claimed is:
 1. An interactive television system comprising: asubscriber television reception system for receiving interactivetelevision programming, the interactive television programmingcomprising one or more interactive television program signals placed atone or more communication frequencies, each interactive televisionprogram signal comprising a data stream containing a plurality ofdigitally compressed video signals, the reception system comprising: auser interface for receiving subscriber selections; a microprocessor,connected to the user interface, for selecting one of the video signalsand directing a seamless switch to the selected video signal; amulti-frequency receiver, for tuning to one or more frequencies anddemodulating an interactive television program signal on the tuned-tofrequency; a means for demultiplexing the demodulated interactivetelevision program signal to obtain a selected video signal; a memoryfor storing the selected video signal; and a decompressor/decoder fordecompressing the selected video signal and converting the decompressedvideo signal into an analog television signal; a means for displayingthe selected video signal, wherein the seamless switch results in atransition to the selected video signal on the display means without avisually perceptible delay; and wherein subscribers in said interactivetelevision system independently select and view said interactivetelevision programming.
 2. An interactive television system comprising:a subscriber television reception system for receiving interactivetelevision programming, the interactive television programmingcomprising one or more interactive television program signals placed atone or more communication frequencies, each interactive televisionprogram signal comprising a data stream containing a plurality ofdigitally compressed video signals, the reception system comprising: auser interface for receiving subscriber selections; a microprocessor,connected to the user interface for selecting one of the video signalsand directing a seamless switch to the selected video signal, whereinthe seamless switch results in a transition to the selected video signalwithout a visually perceptible delay; a multi-frequency receiver fortuning to one or more frequencies and receiving an interactivetelevision program signal on the tuned-to frequency; a means fordemultiplexing the received interactive television program signal toobtain selected video signals; a memory, connected to the demultiplexingmeans, for storing the demultiplexed video signals, the memorycontaining a pointer under microprocessor control which identifies thememory contents to be output; a decompressor/decoder, connected to thememory, for decompressing the stored video signals and converting thedecompressed signals into standard video signals; a RF encoder,connected to the decompressor/decoder, for encoding the standard videosignals into standard video broadcast signals; and a synchronizingmeans, for generating synchronization pulses; a means, connected to theRF encoder, for displaying said selected video signals; and whereinsubscribers in said interactive television system independently selectand view said interactive television programming.
 3. The interactivetelevision system of claim 2, wherein the memory means is a buffer,wherein the microprocessor monitors the contents of the buffer todetermine the identity of the stored video signals, and wherein thepointer is positioned at the selected video signal only when there isenough stored information to enable the decompression and decoding ofthe selected video signal.
 4. A method of receiving and viewing aninteractive television program, where the interactive program iscomprised of one or more interactive program signals located on one ormore communication frequencies, wherein the interactive program signalscomprise digitally compressed video signals containing video and commandinformation, the method comprising the steps of: receiving aninteractive program signal; demultiplexing the received interactiveprogram signal to obtain digitally compressed video signals; storing thedigitally compressed video signals in at least one memory with at leastone memory output; decompressing the demultiplexed digitally compressedvideo signals to obtain the command information; receiving user inputsrelating to interactive program choices; and processing the commandinformation and the received user inputs to obtain a selected videosignal; determining a switch time when the current video signals may beseamlessly replaced with the selected video signal, wherein seamlessswitch results in a transition to the selected video signal without avisually perceptible delay; switching, at the switch time, to a memoryoutput for the selected video signal so that the selected video signalis output and a seamless switch from current video signals to theselected video signal results; and displaying the selected videosignal;.
 5. A method of receiving and viewing an interactive televisionprogram, where the interactive program is comprised of one or moreinteractive program signals located on one or more communicationfrequencies, wherein the interactive program signals comprise digitallycompressed video signals containing video and command information, themethod comprising the steps of: receiving one or more interactiveselections from a user; receiving an interactive program signal;demultiplexing the received interactive program signal to obtain acompressed video signal; storing the compressed video signal in amemory; outputting contents of the memory at a location indicated by amemory pointer, wherein the pointer successively points from olderstored memory contents to the more recently stored memory contents;decompressing and decoding the memory output in a decompressor/decoderto obtain a standard video signal, the decompressor/decoder requiring apredetermined number of video signals before the step of decompressingand decoding may begin; RF encoding the standard video signal to obtaina standard video broadcast signal; controlling the memory, memorypointer, RF demodulator, and demultiplexer to seamlessly switch betweenvideo signals, wherein seamless switch results in a transition to thestandard video signal without a visually perceptible delay; anddisplaying the standard video broadcast signal on a television.
 6. Themethod of claim 5 wherein the step of controlling further comprises thesteps of: managing the memory contents, comprising the steps of:buffering the memory so that the contents of the memory shift tooverwrite the memory location that was most recently output; alteringfilling and emptying rates of the buffering step so that the pointer maybe reset to a predetermined location.
 7. An interactive televisionsystem comprising: a means for receiving user selections; a means forreceiving digitally compressed interactive television programming, theinteractive television programming comprising a plurality of videosignals related in time and content; a means, connected to the receivingmeans, for providing selected video signals, the selected video signalsbased on the user selections; a memory, connected to the providingmeans, for storing the selected video signals; a means, connected to thememory means, for outputting an analog video signal based on the memorycontents; synchronization means, connected to the outputting means, forsynchronizing the analog video signal; a means, connected to thesynchronization means, for encoding the synchronized analog video signalinto a format compatible with a television display; processor means,connected to the memory means, for controlling the output of the memoryso that the memory seamlessly switches between selected video signals,wherein the seamless switch results in a transition between the videosignals without a visually perceptible delay; and wherein the encodedsignal is related to the user's selections and the user mayinteractively and seamlessly switch between video signals.